The present invention relates to a process taking place within and in the environment of a condensate gas or natural gas well for the use and regeneration of additives inhibiting hydrates and/or corrosion for the transportation and treatment or processing of the natural gas from said well to a reception and treatment or processing terminal.
In the case of the production of natural gas in a difficult area, i.e. in the ocean or on land in remote or relatively inaccessible areas, producing companies attempt to transport the gas, which can be produced in different wells and is then collected, to a central processing and conditioning site following a minimum of transformations and/or prior treatment, so as to minimize capital and exploitation costs. This amounts to reducing the operations on the production site to what is strictly necessary to ensure that the transportation of the gas by a gas pipeline to the processing site can take place safely. Thus, certain constituents of the natural gas, namely water and acid gases (CO.sub.2, H.sub.2 S) require special precautions.
As water is present in the deposit, the natural gas is saturated with water at the production temperature. During transportation, the gas normally undergoes a pressure drop, which brings about condensation of part of the water, but in certain circumstances this can also give rise to the formation of hydrate crystals, which are inclusion compounds of hydrocarbon molecules in crystalline structures formed by water molecules and which form at a temperature well above 0.degree. C. However, the formation of hydrates in a gas pipeline can lead to blockages and to production stoppages. To avoid this, it is necessary either to dehydrate the gas prior to its transportation, or inject into the gas a hydrate inhibitor such as methanol or ethylene glycol. In the first case, the gas is generally treated in a washing unit by glycol in order to adjust the water dew point to the value imposed for transportation, the latter taking place under single-phase conditions. In the second case, the inhibitor is introduced into the gas just after the well head and transportation takes place at least partially under two-phase conditions.
Most natural gases contain in varying proportions acid gases, i.e. CO.sub.2 and/or H.sub.2 S, which cannot generally be separated at the production site and must therefore be transported with the gas. However, acid gases give rise to corrosion in the pipelines, particularly in the presence of water. Therefore, as from the well head it is necessary to inject corrosion inhibitors into the gas so as to protect the pipes, because in the long term corrosion can give rise to pipe fractures or significant gas leaks. These corrosion inhibitors are injected in trace amounts, but as they are generally expensive products, they contribute to increasing the gas production costs.
On arriving at the processing site, the gas, which may come from several different wells and is collected in the same gas pipeline, is generally dehydrated in order to obtain a water dew point lower than that required for transportation purposes. This second dehydration stage can be performed in most cases either by an absorption of the water in glycol, or by an adsorption of the water on molecular sieves. Thus, this dehydration process can differ from that used at the production site in order to ensure the water dew point necessary for transportation purposes. This second dehydration stage is indispensable if it is wished to be able to cool the gas to a relatively low temperature, which can e.g. be between -10 and -40.degree. C. with a view to extracting therefrom the natural gas liquids, i.e. hydrocarbons other than methane, which can be supplied in liquid form at ambient temperature. Under these conditions the additives which have been injected for transportation purposes (corrosion and hydrate formation inhibitors) are absorbed during the treatment and are not recycled.
The prior art is illustrated by U.S. Pat. Nos. 4,456,067, 3,348,614, and 4,416,333 and in particular FR-A-2 657 416, which describes a contact zone of a natural gas passing out of a well with anti-hydrate and/or anti-corrosion additives located outside said well. The installation of said contact zone in hostile environments, e.g. in the ocean, still causes technical problems which are difficult to solve.